Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 250031 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 831 PM EDT Wed Aug 24 2016 .SYNOPSIS... High pressure remains over the region through Thursday. A cold front will cross the region on Friday. High pressure will return for the weekend. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
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High pressure will remain centered just off the Mid-Atlantic coast tonight. A light southerly flow will continue during this time...allowing for slightly warmer conditions tonight compared to recent nights. Min temps will range from the lower to middle 60s in the Potomac Highlands to the upper 60s near Washington and Baltimore. Moisture advection will develop ahead of weak shortwave energy overnight. This will cause scattered clouds...but dry conditions will likely persist since shortwave energy and lift will be weak.
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&& .SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY NIGHT/...
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As the theta-e ridge strengthens over the forecast area, a ribbon of instability will work its way up the Appalachians during the afternoon Thursday and spread east in the evening. The added warmth, instability, and terrain circulations suggest that thunderstorms should be able to develop by midday in the mountains and spread east during the afternoon. Believe the initial storms will be confined to points west of the Blue Ridge due to limited CAPE east of there. When the instability improves along I-95, daytime heating will be dwindling. Therefore, will keep chance PoPs west but only slight chance to the east. Think the overnight hours should be dry in spite of low level confluence. The latest solutions (12z 24th) as a bit quicker in taking the surface front through the forecast area (am hesitant to call it a cold front). There is rather strong subsidence from the mid level (h8-5) ridge, leading to rather poor lapse rates. But, there will be a boundary lingering coincident with a hot and reasonably humid air mass. Therefore, have painted in a corridor of 20 PoPs across the central Shenandoah valley up along I-95. Have low confidence in storms firing, but 1 or 2 may. As mentioned, temperatures will slowly be warming through the period. Friday will be the warmest of the week, with temperature likely reaching 90 degrees tomorrow and into the mid 90s Friday.
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&& .LONG TERM /SATURDAY THROUGH WEDNESDAY/...
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High pressure will build in behind the front Saturday and Saturday night. Drier and slightly cooler air expected. Temperatures will be closer to normal. This high will move east and weaken Sunday and Sunday night. Dry conditions will prevail Sunday. We can`t rule out a shower or thunderstorm in the Potomac Highlands Sunday night as the next cold front moves across the lower Great Lakes. Temperatures remaining near normal. A weak cool front will move across the region Monday and Monday night. A chance of showers and thunderstorms will ensue through the period. Temperatures normal. The front is expected to stall Tuesday. Showers and thunderstorms could become more prominent. Temperatures a couple of degrees warmer. A shower or thunderstorm could linger in the region Wednesday as a weak disturbance rides along the stalled front. Temperatures a few degrees above normal.
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&& .AVIATION /00Z THURSDAY THROUGH MONDAY/... VFR conditions expected tonight into tomorrow morning. Scattered clouds (FL050) and south winds (at or below 10 kt) should prevent fog development overnight. There will be increasing instability on Thursday. Anticipate thunderstorms will develop over the mountains during the midday and spread east in the afternoon. MRB most likely to be affected. However, there will be limited forcing east of the Blue Ridge. Therefore strength/coverage concerns raises doubts whether any airfield would receive an impact. A weak cold front will cross the terminals Friday. Winds may shift more to the west, but the front otherwise will be hard to distinguish. An isolated thunderstorm would be possible, but have low confidence in that forecast. VFR conditions expected Friday night. A brief period of MVFR or IFR is possible in any isolated thunderstorms near CHO and mainly Friday evening. VFR conditions at all terminals Saturday and Saturday night. Winds northwest around 5 knots Friday and Friday night. Winds becoming northeast at 5 knots Saturday, then southeast at 5 knots Saturday night. && .MARINE...
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Southerly flow will continue through Thursday night. Winds may channel up the Bay and lower tidal Potomac River tonight into Thursday. This will cause gusts around 15 knots. Isolated gusts around 20 knots are possible...but gusts have been capped around 15 knots for now due to the weaker pressure gradient. The increase in speeds will be more noticeable Thursday evening due to channeling. Will be raising a Small Craft Advisory for portions of the mid Bay. Winds will be veering west Friday as a weak surface boundary crosses the waters, eventually becoming northwest by late in the day.
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&& .TIDES/COASTAL FLOODING... Increased southerly flow will cause water levels to rise tonight into Thursday. By Thursday night, caution stage will be reached at several sites on the Bay. Annapolis could approach minor flood, although not all guidance sources support that solution. Winds will become west on Friday, so there should not be a concern beyond the Thursday night cycle. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory from 6 PM Thursday to 2 AM EDT Friday for ANZ532>534-543. && $$ SYNOPSIS...RCM NEAR TERM...BJL/HTS SHORT TERM...HTS LONG TERM...KLW AVIATION...HTS/KLW MARINE...BJL/HTS/KLW TIDES/COASTAL FLOODING...HTS

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